Radon poisoning arises from uranium (U) and thorium (Th), two of the most widely dispersed radioactive elements in the environment nationwide. For example, in the Navajo nation mining operations (1944-1989) covering four southwestern states, death rates from poisoning are found to be 3.3 times higher than the U.S. average. The uranium decay chain results in several daughter radionuclides such as 226Ra, 222Rn, 218Po, 214Po, 210Po, etc., all of which are in solid form except for radon (Rn), which is a heavy gas that can permeate the ground and enter into dwellings and get inhaled. FIG. 1 shows the 222Rn decay chain (Note: 220Rn from the Th decay chain is referred to as thoron; hereafter, we shall refer to Rn as meaning both, 222Rn and 220Rn). Some of the Rn daughter products decay by beta-gamma ray radiation. However, from a health perspective, it is the alpha radiation emitting radionuclides (e.g., 222Rn, 210Po, 220Rn) which cause the most severe health consequences due to their 100 to 1000-fold higher damage to cells. Rn poisoning via gas seeping through basements, from walls, or degassing from water during showering in U.S. homes results in over 21,000 deaths annually according to the Environmental Protection Agency (EPA). This is far greater than deaths from fires (about 3,000/y) or carbon monoxide poisoning (about 500/y).
Rn (an energetic alpha radiation emitter) is an odorless, colorless gas that kills silently most often in homes. Despite this, our society has become complacent with these deaths because reliable Rn monitoring systems are costly (about $10,000 to over $50,000). In addition their use requires time-consuming steps for Rn gathering in canisters over weeks to months which then must be assayed by trained specialists at off-site laboratories. Rn levels can fluctuate even daily due to which continual monitoring through the year is recommended. Even use of seemingly inexpensive ($50-$100) charcoal canisters for week-averaged localized monitoring can actually add up to $5,000 annually. This process is complicated by the fact that it is subject to tampering via intentional venting during lengthy sample collection by unscrupulous agents to skew results to avoid costly remediation and to provide false assurances to potential home buyers.
It is well known that the massive damage caused by an energetic alpha particle on to the DNA of cells amounts to a zero dose threshold for risk to humans. The chronic intake at even trace levels (in parts per million to billion and even quadrillion) can lead to detrimental health consequences and cancer deaths. Indeed, only about 4 pCi/L (about 4×10−17 g/L) of radon in air constitutes the EPA action limit. A recent New York Times Op-Ed article (Field, 2012) highlights the issue even further as having been grossly underestimated and far more prevalent than thought in society. Radon is thought to be a threat for over 70,000 schools and colleges besides homes and buildings in the environment. Recently, the EPA proposed a rule for communities that mandate monitoring of radon in well water to ensure levels remain below 300 pCi/L as a maximum control level (MCL) when multimedia mitigation programs are in place. If multimedia mitigation programs are not in place, radon in water is monitored to ensure Rn levels are below 4,000 pCi/L as an alternate MCL.
Unlike mandates for smoke and now carbon monoxide detectors for all new homes, there are no regulations mandating in-situ Rn monitors in homes due mainly to affordability and complexity of such a regulation. A cost-effective, high efficiency, real-time sensor similar in scope to smoke or carbon-monoxide detectors could result in alerting dwellers to the presence of Rn above safe levels such that timely findings and remediation can take place.
Unfortunately, at present, people generally find that they have been exposed to lethal levels of Rn after the existence of Rn daughter products are discovered in a biopsy that has revealed terminal lung cancer. An improved, radon sensor technology is needed. Ideally, the sensor will be portable and quick (within tens of minutes) to use providing radon measurements in real time or close to real time.